#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>

double x = 0.0;
double y = 0.0;
double th = 0.0;
double vx = 0.0;
double vy = 0.0;
double vth = 0.0;
void callback(const geometry_msgs::Twist& cmd_vel)
{
    vx = cmd_vel.linear.x;
    vy= cmd_vel.linear.y;
    vth= cmd_vel.angular.z;
}
int main(int argc, char** argv)
{
    ros::init(argc, argv, "odometry_publisher");
    ros::NodeHandle n;
    ros::Publisher odom_pub = n.advertise<nav_msgs::Odometry>("odom", 50);
    ros::Subscriber sub= n.subscribe("cmd_vel",1000,callback);
    tf::TransformBroadcaster odom_broadcaster;

    ros::Time current_time, last_time;
    current_time = ros::Time::now();
    last_time = ros::Time::now();
    ros::Rate r(10.0);

    while(n.ok()){
        ros::spinOnce();               // check for incoming messages
        current_time = ros::Time::now();
        //compute odometry in a typical way given the velocities of the robot
        double dt = (current_time - last_time).toSec();
        double delta_x = (vx * cos(th) - vy * sin(th)) * dt;
        double delta_y = (vx * sin(th) + vy * cos(th)) * dt;
        double delta_th = vth * dt;
        x += delta_x;
        y += delta_y;
        th += delta_th;
        //since all odometry is 6DOF we'll need a quaternion created from yaw
        geometry_msgs::Quaternion odom_quat = tf::createQuaternionMsgFromYaw(th);
        //first, we'll publish the transform over tf
        geometry_msgs::TransformStamped odom_trans;
        odom_trans.header.stamp = current_time;
        odom_trans.header.frame_id = "odom";
        odom_trans.child_frame_id = "base_link";

        odom_trans.transform.translation.x = x;
        odom_trans.transform.translation.y = y;
        odom_trans.transform.translation.z = 0.0;
        odom_trans.transform.rotation = odom_quat;
        //send the transform
        odom_broadcaster.sendTransform(odom_trans);
        //next, we'll publish the odometry message over ROS
        nav_msgs::Odometry odom;
        odom.header.stamp = current_time;
        odom.header.frame_id = "odom";
        //set the position
        odom.pose.pose.position.x = x;
        odom.pose.pose.position.y = y;
        odom.pose.pose.position.z = 0.0;
        odom.pose.pose.orientation = odom_quat;
        //set the velocity
        odom.child_frame_id = "base_link";
        odom.twist.twist.linear.x = vx;
        odom.twist.twist.linear.y = vy;
        odom.twist.twist.angular.z = vth;
        //publish the message
        odom_pub.publish(odom);
        last_time = current_time;
        r.sleep();
    }
}
